The invention relates to an open roof construction for a vehicle having a roof opening which can be closed by a panel of which at least the rear edge can be pivoted upward and downward, and wherein a body for locally influencing the air flow is provided on the underside of said panel, near said rear edge.
In an open roof construction of the type to which the present invention relates, which comprises a panel whose rear edge can be pivoted upward and downward (a so-called tilt panel), objectionable noises, in particular whistling noises, are produced in the open position of the panel. These noises, which depend on the pivoting angle and the driving speed of the vehicle, among other things, are produced especially (but not exclusively) during the first stage of pivoting the panel from the closed position to an open position. The noises that are produced are highly objectionable to the occupants of the vehicle. The cause of the objectionable noises is to be found inter alia in the underpressure generated above the roof of the vehicle as a result of the air flow over the panel, which causes the air to be drawn out from the interior of the vehicle through a gap that is formed at the location of the upwardly pivoted rear edge of the panel.
In the past, attempts have been made to prevent the occurrence of these objectionable noises. German patent no. 4016791 discloses an open roof construction for a vehicle, wherein the means for locally influencing the air flow is made up of a strip projecting downwards near the rear edge of the panel, on the free ends of which projections are present for influencing the air flow. The function of the strip provided with projections is to disturb coherent flow structures through the aforesaid gap. The means used in this prior art solution has a substantially two-dimensional shape (after all, with a minimum dimension in the direction of flow), whose dimension in a direction perpendicular to the panel surface is considerable. Accordingly, one drawback of this prior art solution is the fact that the obstruction in the gap that is formed by said means needs to be compensated by a greater pivoting movement of the rear edge of the panel if it is desired to maintain an unchanged effective gap between the rear edge of the panel and the roof of the vehicle. The increased pivotability, however, makes it necessary to adapt the technical construction of the panel (in particular the parts thereof that are to effect the movement of the panel) with all the concomitant drawbacks thereof (among which an increased space requirement for construction parts, higher cost, etc.).
An open roof construction according to an aspect of the present invention has at least one three-dimensional body that generates swirls in the air flow. The term xe2x80x9cthree-dimensional bodyxe2x80x9d is used to indicate the difference with the prior art, wherein said means described above has a substantially two-dimensional plate-shaped part. According to the present invention, on the other hand, a three-dimensional body is used, wherein the third dimension, seen in the direction of flow, is considerable. In particular, it is this dimension, in the direction of flow, that contributes to the generation of swirls in the air flow. The swirls disturb the air flow to such an extent that objectionable background noises, such as whistling, do not occur.
In one embodiment of the open roof construction according to the present invention, the height of the three-dimensional body, measured in a direction perpendicular to the panel, is in an order of approximately three times the thickness of the panel. In this embodiment, the obstruction of the flow that is caused by the three-dimensional body is minimized, so that minimal adaptation, if any, of the pivoting height of the rear edge of the panel is required. Furthermore it is advantageous with regard to the generation of swirls if the three-dimensional body includes at least one windward surface (i.e. facing towards the air flow) and at least one leeward surface (i.e. facing away from the air flow). The generation of swirls takes place at the transition between the two surfaces. In a further embodiment, of at least a portion of one or all of the windward and leeward surfaces is oriented obliquely to the surface of the panel.
In another embodiment, the three-dimensional body includes sharp transition edges between a respective windward surface and a respective leeward surface on its rear side, seen in the direction of flow, wherein the edges include an angle with the direction of flow.
As a result of said angle (which may have any desired value), swirls are generated in the air flow at the location of said sharp transition edges, which swirls lead to the formation of so-called vortex streets. The dimensions of the vortex streets depend on the location on the transition edge where the swirls are generated. The location where the swirls are generated can be altered to cover a large range of frequencies (with respect to the objectionable background noises that occur) and prevent objectionable background noises occurring over the entire frequency range. In the case of small panel openings, the total swirling of the exiting air flow aids in preventing objectionable noises.
In another embodiment, the three-dimensional body includes windward surfaces and leeward surfaces that gradually blend into one another. A sharply defined transition edge is lacking in this embodiment, however, the (gradual) transition between the windward and leeward surfaces can nevertheless lead to the generation of swirls.
Generally a number of three-dimensional bodies will be arranged beside and/or behind each other. These bodies may or may not be arranged adjacent to each other.
In addition, geometric shapes can be used for the three-dimensional bodies. For example, it is possible to use a three-dimensional body that comprise of a block having a zigzag rear edge and/or front edge, wherein the block extends substantially transverse to the panel. The sharp transition edges that produce the swirling effect are formed at least at the location of said zigzag rear edge and/or front edge.
Another embodiment is a three-dimensional body which comprises a tetrahedron, one surface of which coincides with the underside of the panel having one corner point of the surface pointing in the direction of flow, or in a direction opposite thereto. When the tetrahedron has a corner point of the surface pointing in the direction of flow, the tetrahedron has a windward surface, wherein the windward surface diverges in the direction of flow with respect to the panel surface, with two mutually converging (in the direction of flow) leeward surfaces adjoining the surface. The transition edges between the diverging surface and the two converging surfaces produce a swirling effect. If the corner point of the tetrahedron points in a direction opposite the direction of flow, there are two mutually diverging windward surfaces, and one leeward surface, which converges with respect to the panel surface.
It is also possible to use a so-called NACA vortex turbulator as the three-dimensional body. This is a wedge-shaped body, which was developed by NACA (the predecessor of the present US NASA) for generating swirls.
It is possible to attach the aforesaid three-dimensional bodies to an existing panel after manufacture, but it is also possible to form the bodies thereon during the production stage. In the latter case, the three-dimensional body can be integral with the panel. Thus the three-dimensional body may form part of the so-called panel encapsulation, which forms the underside (interior side) of the panel.